# Evaluation Indices: Matching Ratio

May 20, 2023

Matching Ratio is a popular evaluation index used in the field of image processing and computer vision for tasks such as image recognition, object detection, and image segmentation. The Matching Ratio provides an objective measure to evaluate the accuracy of the matching algorithm.

## Definition

The Matching Ratio is a similarity measure used to evaluate the performance of image matching algorithms. It is the ratio of the number of correct matches to the total number of matches. In other words, it measures the percentage of correct matches out of all the matches made by the algorithm. The Matching Ratio is calculated as follows:



$$Matching Ratio = Number of Correct Matches / Total Number of Matches$$

The Matching Ratio ranges from 0 to 1, where 1 indicates that all matches made by the algorithm are correct, and 0 indicates that none of the matches are correct.

## Applications

Matching Ratio is widely used in computer vision applications such as image recognition, object detection, and image segmentation. It is used to evaluate the accuracy of the matching algorithm in these applications.

For example, in image recognition, the Matching Ratio is used to evaluate the accuracy of the algorithm in identifying objects in an image. In object detection, the Matching Ratio is used to evaluate the accuracy of the algorithm in detecting objects in an image. In image segmentation, the Matching Ratio is used to evaluate the accuracy of the algorithm in segmenting an image into different regions.

## Limitations

Although the Matching Ratio is a widely used evaluation index, it has certain limitations. One limitation is that it only measures the accuracy of the matching algorithm and does not take into account other factors such as the speed and computational complexity of the algorithm.

Another limitation of the Matching Ratio is that it does not provide information about the quality of the matches made by the algorithm. For example, an algorithm may make correct matches but may also make some incorrect matches that are of poor quality.

## Examples

Let’s consider an example to illustrate the concept of Matching Ratio. Suppose we have two images, A and B, and we want to find the matching keypoints between these two images using an algorithm. Let’s assume that the algorithm finds a total of 1000 keypoints and makes 800 matches.

Out of these 800 matches, 700 matches are correct, and 100 matches are incorrect. The Matching Ratio for this algorithm would be:

Matching Ratio = Number of Correct Matches / Total Number of Matches
Matching Ratio = 700 / 800
Matching Ratio = 0.875

This means that the algorithm has a Matching Ratio of 0.875, which indicates that it has correctly matched 87.5% of the keypoints between the two images.